A variety of artificial materials for human tissue volume replacement have been developed and practically used in diverse applications, however, these involve a significant problem of gradual volume reduction.
Allogenic dermis or allogenic bone of human or animal origin has been used as a transplant material after processing the same. However, the process thereof is complicated and causes extended time consumption to get permission from authorities since various chemical methods are additionally applied to the processing to eliminate antigenicity of human immune proteins and cells. Also, the processing has other disadvantages in that this cannot completely eliminate antigenicity to cause adverse side effects, requires considerable processing costs, and the supply of cadaver as raw material is limited and thus cadaver is being purchased at the high price of 500,000 won per 1 cc of the cadaver.
A variety of artificial skin equivalents are now being developed, more particularly, many products such as acellular artificial skin, hierarchically layered (a two-layer structure of) cellular living skin equivalents (LSE) prepared by culturing epidermal and dermal cells of a patient oneself, etc. were developed and they are in the pre-commercial phase. Such products are very expensive since they are manufactured by decellularizing allogenic tissue or using biomaterials such as collagen.
Cellular artificial skin derived from human bodies has excellent wound recovery effect in the qualitative aspect of medical treatment, for example, rapid wound healing, scar reduction and so on. This artificial skin is also reported to exhibit no immune rejection response caused by autologous cells or processed allogenic tissues.
Matrix-type artificial skins using chitosan, collagen, chitin, etc. are commercialized and alternative skins, which were newly developed by culturing skin cells on the matrix, are now in clinical trials. However, mass production of these products has not been accomplished.
Korean Patent No. 10-0469661 disclosed a method for preparing an acellular dermal graft to manufacture and provide a product named “SureDerm”, thus achieving domestic production of some of biomaterials for tissue regeneration, which have usually been imported from overseas.
However, since there are many restrictions in securing domestic supply of human skins, raw materials are mostly imported to manufacture artificial skin products.
In general, the above artificial skin products referred to as “filler” are usually manufactured using animal-derived materials, synthetic materials and human-derived tissues as raw materials, but they have several disadvantages in terms of convenience of use, durability and price thereof.
Another products include, for example: ZYDERM® for injection manufactured using bovine collagen; ARTECOLL® which is a mixture of polymethyl methacrylate beads suspended in collagen; RESTYLANE® which is a modified hyaluronic acid; CYMETRA® is a powdered form of ALLODERM®, and the like.
ALLODERM® commercially available from LifeCell is a human allogenic acellular dermal matrix prepared by decellularization of cadaver dermis, and is used as a graft or an insert. This product has advantages of; completely eliminating the possibility of immune rejection by removing all of cells from raw material; and exhibiting high biocompatibility compared to any other conventional artificial skin product due to use of natural human tissue. Accordingly similar products have also been developed in domestic fields, but it is difficult to find skin donors, thus resulting in import of raw materials from overseas.
Generally, fat tissue extracted from obese patients is discarded or partially stored for further use. Triacylglycerol in lipid droplets, which is contained in a great amount in tissue, or neutral lipids such as sterol esters may be deteriorated by oxidation or partial oxidation and hydrolysis, so that it is difficult to store fat tissue for over 2 months to reuse.
Lipid oxidation causes discoloration or lipid loss by a reaction between a reactant obtained through oxidation of polyunsaturated fatty acid and amino compounds such as proteins, and generates toxic materials such as hydroperoxide, unsaturated aldehyde, etc. Furthermore, fat tissue from animals excluding humans, for example, pigs or cows, etc, has low liquid lipid content (50 to 70%), and is partially mixed with panniculus muscularis. On the other hand, human fat tissue is clearly distinguished from dermal tissue or muscle layer and has exceedingly high content of liquid lipid and thus there has not yet been any attempt to develop a novel biological graft material by processing human fat tissue.
Meanwhile, an artificial substrate means a support material capable of forming a three-dimensional matrix into which tissue cells taken from a donor were seeded, and are often referred to as carriers or artificial scaffolds. Such scaffolds must satisfy the following conditions:
First, the scaffolds should maintain the morphological structure of biotissues to be regenerated; second, they should efficiently induce adhesion, growth and differentiation of cells to be cultured; third, they should exhibit high biocompatibility; forth, they must be safely absorbed and degraded in vivo after completion of the scaffolding. For the development of technologies for an ultra-precision three dimensional artificial scaffold to regenerate biotissues, manufacturing artificial scaffolds for tissue regeneration to efficiently differentiate into specific tissue cells and producing biocompatible materials substantially similar to the biotissues are two key technologies.
For example, scaffolds for bone and soft tissue regeneration include various synthetic materials such as synthetic or natural calcium phosphate, polylactic acid or polyglycolic acid; collagen; and cellulose based natural polymers, etc. Materials used to manufacture scaffolds for facilitating tissue regeneration must have microstructure and chemical composition suitable for optimal cell growth and cell function. For bone regeneration, these materials must have similar physical, chemical and mechanical properties to the host bone because such properties may influence normal bone growth and bone function. Recently, a lot of studies on natural polymers have been carried out, and particularly, there are many researches on the use of chitosan and biological materials.
However, since there is a limitation in the use of tissue-compatible biomaterials which are decomposed in vivo, and tissue engineering technologies enabling differentiation into various body tissues are still insufficient, there are limitations in reproducibility of the function of each organ in human body.
In addition, although tissue-compatible micropowder is being used as a micropowder for three-dimensional cell culture, biocompatible materials such as poly L-lactic acid(PLLA), poly lactic-co-glycolic acid(PLGA), which are used as a micropowder for cell culture, cost more than 500,000 won per 1 g of material. In particular, for cell culture, a structure similar to that of human tissue should be formed, but high precision molding is not developed sufficiently enough to form a human tissue-like structure.
The biomaterials used in biodegradable micropowders such as polylactic acid(PLA), polyglycolic acid(PGA), etc. to manufacture artificial scaffolds are prepared by conventional processes including, for example: gas foaming/salt leaching; high pressure gas expansion; emulsion freeze-drying; solvent-casting/particulate leaching technique; phase separation, and the like.
However, these processes have drawbacks such as low reproducibility and limitation in manufacturing high precision and complex three-dimensional structures. Additionally, in case of manufacturing porous structures, the above processes have problems in that it is difficult to freely control pore size and porosity, they show low interconnectivity between pores, thus causing difficulties in cell growth, nutrition supply, diffusion and transfer of cells into artificial scaffolds and an extended period of time for production thereof is required.
Fat tissue has difficulties in storage or transplantation since it consists of liquid lipid which amounts to 98% of the total tissue volume, and involves all variables upon cell culture such that there has been no attempt to develop materials for transplantation using fat tissue.
However, fat tissue volume can be partially maintained if lipids are removed from fat tissue while maintaining microstructure thereof. Accordingly, it is assumed that fat tissue can play a significant role as a biomaterial.
Recently, there are some reports disclosing that a sponge-like structure promotes the growth and differentiation of cells. Based on this fact, it is assumed that the volume of material to be transplanted into a human body is more important than the weight of the same in terms of in vivo effects or cell culture.
Consequently, it is expected that fat tissue can be a remarkably beneficial material compared to other biotissues if the fat tissue can maintain microstructures of connective tissue and cell membrane during adipose tissue processing.
Accordingly, the present inventors have made extensive efforts to develop a sponge-like powder with three-dimensional structure, in which the volume of fat tissue is maintained at maximum possible size, lipid oxidation is prevented, and disadvantages of the existing artificial scaffolds are complemented, and as a result, they confirmed that when adipose tissue lipids are physically removed and dried, the fat tissue can be used as scaffolds for human tissue volume replacement by injecting them for transplantation and at the same time, can be used as scaffolds for cell culture, thereby completing the present invention.